Deviation correction for cathoderay beams



Jan.4, 3949. A. c:. MuNsTER ET AL '2,458,291

' DEvIATIoN-CORRECTION FOR cATHoDE-RAY BEAMS Filed Nov. 25, 1946 2 Sheets-Sheet 1 Jan. 4, 1949. A. c. MUNSTER ET AL 2,458,291

DE'VIATION CORRECTION FOR CTHODE-RAY BEAMS vFiled. NOV. 25, 1946 I 2 Sheets-*Sheet 2 @www g Aci/vr;

Patented jan., 4, 1.949

DEVIATION CORRECTION FOR CTHODE- RAY BE-AMS Allen C. Munster, Philadelphia., and David E. Sunsten, Cynwyd, Pa., assignors to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application November 23,'"li946, serial No. 711,968

' 8 Claims. l

The invention 4described and claimed herein relates to control means for cathode-ray tubes. More particularly, the invention provides automatic control means for correcting, substantially (Cl. S15-21) ""stantially corrected.l

It is a more spec'ii'lc object of this invention to provide means in a television system for corinstantaneously, anunintended deviation in the 5 recting, substantially instantaneously, unwanted position ofthe beam. vertical deviations of a cathode-ray beam from The present invention is of particular utility 'f a preselected scanning pattern comprised of a in television systems where it may be convenientplurality of vertically-displaced lateral scanning ly employed to correct an undesired departure of lines. the spot of the scanning electron beam from a It is a still more specic object of this invenpreselected path the beam is intended to follow. tion to provide scanning-beam control means Control of this nature is particularly desirable adapted to function in a selective manner to in multi-color television systems employing a maintain accuracy of beam position in a telecathode-ray tube having a multi-color striped or vision system employing an interlaced scanning mosaic-line screen, or in three-dimensional telel5 pattern. vision systems employing a cathode-ray tube These and other objects, features and advanhaving differently polarized screen elements in tages of the present invention will be clear from striped arrangement, since deviation of the scana consideration of the following detailed; dening spot from its intended scanning path introscription taken in conjunction with the accom duces error in the picture being viewed which panying drawings, in which may be noticeable and objectionable. Figure lis an illustration, partly schematic, In black and white television systems employpartly diagrammatic, of a cathode-ray tube and ing a conventional scanning pattern comprised associated circuit employing one embodiment of of a plurality of vertically-displaced parallel latthe invention; eral lines, the beam spot of the viewing tube may Figure 2 is an illustration of a cathode-ray tube deviate vertically from its scanning path a limemploying an alternate arrangement of control ited amount without the effect of such deviation elements; being noticeable to the observer. But inmulti- Figure 3 is a schematic representation of an color or stereoscopic television systems employing arrangement of control elements which may be striped screens, considerably less vertical deviaemployed with the cathode-ray tubes of Figures tion is permissible before the error is noticeable. 1 and 2; In short, for good quality of reproduction in these Figure 4 is another arrangement of control eletypes of color and three-dimensional television ments which may be used in certain applications; systems, it is important that the spot of the and scanning beam adhere closely to the line it is Figure 5 is a schematic representation of a intended to scan. Apparatus which may be satspiral-scan control means. isiactory for controlling the scanning of a black Referring now to Figure l, there is illustrated and white television tube may not be at all satisa cathode-ray system in which conventional cirfactory for controlling the scanning of a multi cuits and well known tube elements are merely color or stereoscopic television tube because of shown in block form. The system is shown as the more rigid requirements of color and threecomprising a source of horizontal deflection sigdimensional presentation. nals It, a source of vertical deflection sig- It is an object of this invention to provide nals II, amplifiers I3 and I4 for the horizontal means for correcting, substantially instantaand vertical deflection signals respectively, a neously, unwanted deviations of a cathode-ray voltage adder I5, and a cathode-ray tube liavbeam from a predetermined and desired condiing conventional cathode il, control grid Id, horim tion with respect to its instantaneous position. zontal deecting means I9, vertical deflecting It is another object of this invention to promeans 29,'l and beam ZI. The screen 23 and com vide means for maintaining a beam of electried trol eements'23 are described in detail later. particles accurately positioned as it is deflected Vertical deflection signals from source II are along a preselected path. applied by Way of voltage adder I5 and amplifier It is another object of this invention to provide I4 to vertical deecting means 2li, and horizonmeans, responsive to an unwanted deviation of an tal d eilecting signals from source I0 are applied electron scanning beam from substantially any through amplifier I3 to horizontal deectine portion of its scanning path, for generating cormeans I9.

rection signals, and for synchronizing the application of the correction signals with the scanning Cathode-ray tube I6 may serve as the viewing vtube vof` a television receiver, or as the camera tube of a television transmitter, or may serve"y other cathode-ray tube functions. For the purpose of facilitating the description of the present invention, cathode ray tube |6 is assumed t-o be the viewing tube of a three-color television receiver having video and blanking signals from source l2 applied to control grid I8. Screen 22 is assumed to be comprised of different fluorescent phosphors arranged in closely-spaced, parallel, lateral lines; adjacent lines are comprised of different phosphors, but every third line is comprised of the same phosphor. Or, alternatively, screen 22 may be comprised of a, common uorescent material, as for example, a white phosphor, to one surface of which color lter material has been applied in closely-spaced, narrow, lateral strips or lines, adjacent strips being different `color filters and every third strip being the same color filter.

In Figure 1, the positions of nine lateral lines of fluorescent screen 22 are shown. These are identified by reference letters a to z' inclusive, and they are intended to be illustrative of the much larger number of lines of which the fluorescent screen of an actual three-color television viewing tube will be comprised.

In accordance with the present invention, control means 23 are associated with screen 22 to provide accuracy of movement of the scanning beam 2|. In one embodiment, illustrated in Figure 1, control means 23 comprises a plurality of closelyspaced, mutually-insulated, conductive strips mounted within the tube between the source of the beam 2| and fluorescent screen 22, one control strip being provided for each scanning-line of the fluorescent screen. The conductive control strips are porous to electrons and may be comprised, for example, of a very thin -coating yof aluminu-m or silver which may be conveniently applied directly to the surface of the fluorescent screen, as by a suitable evaporation process. In such a process, a suitable stencil'or mask may be employed to control the character or configuration of the metal deposit. In the instant embodiment, the configuration is that of a plurality of closely-spaced, vertically-displaced, lateral strips.

In another embodiment of the invention, illustrated schematically in Figure 2, the conductive control strips 63 are applied to the glass face of the cathode-ray tube, and the phosphor of the fluorescent screen is deposited upon the control strips. In this case, the phosphor material 62 is between the electron beam source 51 and control strips 63; hence the phosphor is thinly applied so as to permit a sufficient number of electrons to pass completely therethrough and strike the control strips. If control strips 63 be located between the phosphor material and the eye 64 of a viewer positioned in front of the tube, the control strips are comprised of a very thin application, as for example a thin application of silver, in order to be transparent to light. If the method of image presentation be such that the screen is viewed from the rear, then of course the control strips need not be transparent to light.

Referring now to Figure 3, there is illustrated a schematic plan View of the physical arrangement and electrical connections of the conductive control strips as employed in both of the embodiments described above and illustrated in Figures 1 and 2. The plan view of the control strips is the same irrespective of whether the strips are located in front of, or in back of, the fluorescent screen. In Figure 3, eleven control strips, a.' to i l inclusive, and aa" and ii', are shown and these are intended to be representative of the large number of control strips which will ordinarily be associated with the fluorescent screen. The actual number fof control strips is preferably larger by two than the number of scanning lines in the pattern. In Figures l, 2 and 3, nine of the control strips shown, i, e., strips a to i' inclusive, correspond to the Vnine scanning lines, a to i inclusive, of fluorescent screens 22 and 62 shown in Figures 1 and 2 respectively. The other two strips, aa and ii', are extra control strips, one being provided at the top of the screen and the other at the bottom of the screen. Where the control strips are comprised of thin applications of metal, deposited as yby an evaporation process, the extra strips may .either be deposited directly upon the glass face yof the tube, or additional phosphor may be provided Ato serve as a backing for the metal deposit.

All of the control strips are shown as having a slight downward slope to the right; this corresponds with the customary slope of the scanning lines of fluorescent screens, it being understood that the customary scanning action is from left to right across the image and downward.

Every third control strip is shown to 'be electrically connected to a common lead, thus forming three groups of interlaced control elements. The individual connections from the control strips to the common leads, and also portions of the common leads, may conveniently be comprised of very ne lines of metal deposited by suitable evaporation process.

In Figures 1, 2 and 3 of the drawings, a group comprising control strips a', d', g and ii' are shown connected to common lead R; a second group comprising strips b', e and h are shown connected to common lead B; and a third group i comprising strips aa', c', f and i are shown connected to common lead G. The control strips connected to lead R may be deemed to be associated with the lines of screen 22 which under electron bombardment emit a red color, either as a result of the employment of a red filter or of the employment of a redphosphor. Similarly, the control strips connected to leads B and G may be considered as being associated with blue and green lines, respectively, of screen 22.

Referring again to Figure 1, a suitable positive potential is applied t0 each of the control strips by Way of the common leads R, B, G and resistors 2,4, 25, 2B respectively. Capacitor 5B is a by-pass capacitor. Each of the three leads, R, B and G, is connected to suitable switching means `3|), through which control signals are passed to feedback connections 3| and 32. The control signals referred to are derived from the impingement of electrons of beam 2| upon one of the conductive control strips. For as the impingng elec'- trons return to cathode through one of the resistors 24, 25, 26, a .signal is developed at the Y ungrounded end of the resistor which is available for control purposes.

In order to effectuate the desired control, the switching means provided in the present illustration are adapted to accomplish the following:

. (a) provide an open circuit between each of the strip associated with the line adjacent and below the line intended to be scanned.

The switching means for accomplishing the above may be of any suitable form, preferably electronic. However, for the purpose of describing the instant embodiment, it will sufce to illustrate and describe a mechanical switching arrangement. There is accordingly shown in Figure l, a pair of rotary-type switches 33 and 33, having-rotatable switch arms 35, 36 respectively, and each having three arcuate contactsegments L, M, N and L', M', N' respectively. Each of the three common leads R, B and G, is connected to one of the three segments of each switch. In the illustration, lead R is connected to segments L and L', lead B is connected to segments M and M', and lead G is connected to segments N and N.

Switch arms 35, 33 are ganged together and -are rotated clockwise simultaneously, as by a synchronous motor (not shown), with switch arm 35 lagging switch arm 3B by one segment. The leads of feedback connections 3| and 32 extend from switch arms 35 and 36 to amplifiers 31 and 3B, respectively. These amplifiers are preferably D.C. amplifiers so that the D.C. component of the correction voltage may be preserved. Or, alternatively, means may be included in ampliiiers 31, 3B for accomplishing D.C. insertion.

In the illustrated embodiment now being described, the output signals from amplifier 38 are shown to be inverted in phase inverter 4I, butif desired, the inversion of the signal may of course be accomplished by having amplifier 38 comprise one more, or one less, stage than amplifier 31. The output signals of amplifier 31 and the inverted signals of ampliiier 38 are combined in voltage adder 39 and are applied, by way of common connection 48 and switch S, to voltage adder I5 where they are combined with the vertical deflection signals from source I I.

If desired, the control signals fed back by way of connections 3l and 32 may be applied respectively to opposing plates of the vertical deflecting means, in which ease inversion of the signals or one of tl'e paths, is unnecessary,

The operation of the embodiment of our invention illustrated in Figure 1 will now be described. Beam 2l of tube l5 is moved through a predetermined scanning pattern, as by the application of horizontal and vertical deflecting signals from sources itl and Il to the horizontal and vertical deecting means I9 and 20 respectively.

Assume an instant in the scanning pattern when beam 2l is scanning a blue line as, for example, line b. A portion of theelectrons of beam 2l completely penetrate control strip b and impinge upon the phosphor of line b causing it to glow. The remainder of the beam electrons partially penetrate strip b. Observe that strip b is connected to common lead B and that lead B is connected to segment M of switch 33 and segment M' of switch 34. Assume now that an unavoidable departure occurs in one or more of the potentials determining or iniiuencing vertical deiiection, thus causing beam 2| to deviate in a downward direction from its intended position. In so deviating, some or all of the electrons of beam 2l impinge upon control strip c'; some of these impingent electrons penetrate through strip c', while others penetrate but partially therethrough. Those electrons which impinge upon, but only partially penetrate through, strip c', return to cathode through resistor 26, and a signal is thereby developed across the resistor.

Observe that control strip c is connected to common lead G and that lead G is connected to segment N of switch 33. Rotating switch arm 35 of switch 33. is in contact with segment N and the signal produced across resistor 26 is applied by way of connection 3l to the input circuit of amplifier 31. The voltage developed across the output circuit of amplifier 31 is applied by way of voltage adder 39 and lead 48 to voltage adder l5 Where it is combined with the Vertical deflecting signals from source Il. The gain and phase characteristics of the feedback circuit are so arranged and adjusted that the polarity and magnitude of the voltage delivered by amplifier 31 is eiective to move beam 2| in an upward direction. If desired, the gain and time-delay of the feedback amplier 31 may be so adjusted that the upward correcting movement of beam 2l is suincient to cause the beam to overshoot control strip b', whereupon a portion of the electrons strike control strip a' which is adjacent and above.

It will be observed that when beam 2i deviates downwardly from control strip b to c', no correction signal is obtained from-amplier 38 for the reason that connection 32 is open at switch 34, switch arm 36 being out of ycontact with segment N l It should be mentioned here that they fre'- quency-response characteristics of ampliers 31 and 38 are preferably such that steep wave-front control signals may be passed therethrough, thus permitting the control voltages to reach voltage adder i5 with a minimum of delay.

The correction signal derived is of course a function of the number of electrons impinging upon, but not completely penetrating through, an adjacent control strip. If beam 2l is intensitymodulated, as will ordinarily be the case, then the system preferably is so adjusted that a beam of strong intensity is prevented, by the action of the control signal, from impinging upon an adjacent control strip except for a very small portion of the beam-spot area. However, when the beam is modulated from strong intensity to a weaker intensity, a greater portion of the beam-spot area tends to encroach upon the adjacent control strip. For optimum operation, the system may be so arranged that amplifiers 31 and 38, in addition to having a steep frequency-response characteristic, provide high gain, so that adequate values of c'ontrol voltage may be derived from the impingement of a .relatively vsmall number of electrons upon the adjacent control strips. In other Words, iniaccordance with the method of operation nowbeing described, a given departure of deflection-voltage .causes a beam of strong intensity to encroach upon an adjacent control strip by an extremely small portion of its spot area, while a weaker beam encroaches by a larger, but, tolerable, amount.

An alternate method of compensating for the intensity-modulation of the beam is to apply the video `signals from source l2 exclusive of the blanking signals, as by way of video selector 60 and connection 6I, to amplifiers 31 and 38 to control the gains of the ampliiiers so that, when the beam intensity is low, the amplifier gain is high, thereby maintaining the gain around the feedback loop independent of beam intensity, and

thus maintaining the controlled spot-position substantially independent of beam intensity.

Referring again to Figure 1`, assume now that beam 2| has deviated upwardly from line b,

either as a result of an overshooting control Voltage as mentioned above, kor as a result of an unavoidable departure `in one or more of-the voltages determining vertical deflection. WhenY an upward deviation from line position b occurs,

electrons from beam 2l strike control strip a..

Some of the impingent electrons penetrate com pietely through the strip. Other electrons only partially penetrate strip a and in returning to cathode il these electrons produce a signal across resistor 2.5i to which strip a isy connected by means of common lead R. It will be seen that lead R is connected to segment L of switch 33 and segment L of switch 34. Switch arm 35 .of switch 33 is not in contact with segment L and feedback connection 3l is consequently open at i vertical deiiection signals from source H is to move beam 2i in a downward direction. If desired, the gain and time-delay of amplier 38 may be so adjusted that the downward correcting movement of beam 2l is suflicient to cause the beam to overshoot control strip b', whereupon a portion of the electrons strike control strip c'. If the system be arranged and adjusted to employ overshooting control, then the beam, following an unwanted departure, is given an oscillatory motion for the remainder of the scanning line whose frequency is preferably higher than that of the picture elements, and amplifiers 3l' and 33 are peaked amplifiers adapted tor pass the oscillatory frequency, as well as lower i're" quencies.

Referring again to Figure l, it will be yobserved that when line b is being scanned, the voltage developed across resistor 25, as a result` of electrons impinging upon control strip b and returning to cathode by way of lead B, is not ap.

plied to voltage adder i5 for the reason that both feedback circuits 3l and 32 are open at segments M and M' of switches 33 and 34, respectively..l

It will be understood that the angular positions occupied by switch arms 33 and 36 in Figure l of the drawings assume that line b, or a line of the same iield as b, is being scanned` In order to eiectuate the switching which my novel arrangement requires, switch arms 35, 35

are rotated in coordination with,v the movement of scanning beam 2l, the rotating speed of the switch arms being dependent upon the scanningv pattern being employed. For example, in a three-color system employing an every-thirdline interlaced scanning pattern, switch `arms 35 and 36 of switches 33 and 34 are rotated clockwise, and are so timed as to remain in engagement with each switch segment during the scanning of a eld, i. e. during the scanning of thev lines common to a single color. arm 35 engages segment N and arm 36 engages segment L at the instant that beam 2l" startsto sweep line b. Beam 2| completes scanning of the color field, of which line b is a component,A at the saine instant that rotating arms 35, A36 complete their respective passages over switch.

For example, f

segments N and L', respectively. `Duringl then".

period required for beam 2l to return to line vc at the top of the screen, switchv arms 35, A36 1 traverse the spaces between switch segments N, L and L', M", respectively. 1

to be used with the arrangement illustrated in Figure 1, everythird control strip may be connected to av common lead, just as in the case of every-third-line interlace scanning described above, but if this be done switch elements 35,

should be rotated counterclockwise instead of clockwise, and the speed of rotation should be such that elements 35, 36 sweep over a switch segment during the time required to scan a single line position. This requires a very high rotary speed, well beyond the capabiilties of most mechanical switches, but well within the capabilities of an electronic switching device, as for example, a radial-beam tube. The switching arrangement shown schematically in Figure 1 and :thus far referred to in mechanical terms, may be deemed to be also a schematic representation oi a radial-beam tube in which elements L, M, N andL', M', N', represent separate anodes arranged in circular fashion about cathodes 2l and L12@ respectively, and in which rotating elements 35 and 3 6 represent beams of electrons which are rotated about the axes of the tubes in known mann-er, as by the application of a rotating magnetic and/or electric ield.

Assume now a system as described in the above paragraph, i. e., having an every-other-line interlace scanning pattern and radial-beam tube switches, the beams of which rotate counterclockwise at a speed of one anode for each linescan. Then it may be readily determined from an examination of the circuit of Figure l, that the voltage developed across the resistor corresponding to the line intended to be scanned, is not fed-back to the voltage adder i5 because of the fact that both feedback circuits 3l, 32 are open at the switches. However, for a down ward deviation, it will be observed that a correcting signal-is vfed back by way of connection 3i and amplifier 31, while for an upward devia-- tion, a; correcting signal of opposite polarity is fel 'back by'way of connection 32, amplier 33 and phase inverter 4|.

Ii the control-strip pattern and switching are rangement shown in Figure 1 be employed when the scanningvpattern requires that every line be scannedin sequence, then radial-beam tubes are preferably employed as switches, and the beams represented by switch elements 3E, 36, should be rotated clockwise at a speed of one anode for each line scanned. Il this be done, then control is obtained in a. manner similar to` that described above forevery-th-irddine and every-other-line scanning. y

It is to be understood that our invention is not limited to thespecc pattern of interlaced control lstrips illustrated in Figures 1, 2 and 3.

Other control strip arrangements may of course be used. For example, where an fevery-other-line interlace scanning pattern is to be employed the 9 control means may conveniently take the form shown in Figure 4.

In the arrangement shown in Figure 4 only two groups of control strips are employed. The strips may be in the form of very ne wires positioned along opposite lengthwise edges of the path which the beam is intended to follow, as for example, in the interstices of the scanning lines of the screen of a stripped multi-color viewing tube. The control wires may, if desired, be applied by a suitableI Aevaporation process. Assume that the arrangement shown in Figure 4 is representative of a screen in which dotted line ab represents the first line to be scanned. Control wire aa runs along the upper lengthwise edge of the scanning line and control wire bb runs along the lower lengthwise edge. If desired, the spot of the scanning beam may be of such size that when properly centered upon scanning line ab some of the electrons impinge upon control wire aa and a=z substantially equal number impinge upon control wire bb, thereby generating control voltages of equal magnitude in the two control wires. These equal voltages are fed back by way of connections 3| and 32 and are ap-plied in opposition, as

by the means shown in Figure 1, to maintain the beam spot substantially centered between the two control wires. Upon the completion of the scanning of line ab, line cd is next scanned, and

control is eifectuated by means of control wires il cc and dd, in a manner similar to that just described. Upon completion of the scanning of a iield comprised of alternate lines, the beam is returned to the top of the screen. The first line to be scanned in the new field is that represented by the dot and dash line bc, and control is accomplished by means of wires bb and cc.

With the arrangement of Figure 4, switching is only necessary at the end of each field; hence a pair of two-segment rotary type mechanicall switches 5l, 52 driven at a speed of one revolution per scanning frame are satisfactory.

It is also to be understood that our control system is not limited to scanning patterns in which the lines to be scanned are horizontal, or substantially horizontal, i. e. having'the customary slight downward slope. On the contrary, our system will operate quite satisfactorily with scanning patterns of various congurations, as for example, with a spiral scanning pattern. As will be understood by those skilled in the art, a spiral scanning pattern may be obtained by amplitude-modulating horizontal and vertical deflection signals which are sinusoidal and 90 out of phase. If it be assumed that the horizontal deflection signals provided by source ID of Figure 1 are 90 out of phase with the vertical deflection signals provided by source Il. and that both be sinusoidal, then the modulation necessary for spiral scanning may be provided by anplying a saw-tooth voltage from generator 42 by way of switch W and voltage adder 43, to horizontal and vertical amplifiers I3, I4, so as to control the gain thereof. The control voltages fed back by way of lead 40 may then be apn-lied by way of switch S to the voltage adder 43 to control the accuracy of the radial deflection.

For the control of spiral scanning, two control strips of spiral configuration may be employed, as is illustrated in Figure 5. v'The space vbetween the strips defines the path the beam is intended to follow. If the beam deviates outwardly, electrons impinge upon control strip 1', and the voltage developed across resistor isf-is fed back, as through connection 3| of Figure 1, amplifier 37,

voltage adder 39, conductor 40, and switch S, and is applied to voltage adder 43 to alter the sawtooth wave in desired manner. Similarly, if the beam deviates inwardly, electrons impinge upon target strip t, and the voltage developed across resistor 50 is fed back, as through connection 32 of Figure 1, amplifier 38, phase inverter M, voltage adder 39, conductor 4U and Switchs, and is applied to voltage adder 43. No switching means is required in the spiral scanning arrangement just described It should also be mentioned that, if desired, the saw-tooth generator 2 may be omitted, and the control voltages developed by the impingement of electrons upon strips r and t may be relied upon to maintain the scanning beam in its intended path between the control strips.

Thus far our description of the inventionhas indicated that control strips are provided along both lengthwise edges of the path the beam is intended to follow, thus providing positive control against unwanted deviations in either of two opposing directions.

If desired, control elements may be provided along one edge only of the preselected path of the beam.- In that event, and assuming lateral scanning, the vertical deection signal may be biased to such an extent that, in the absence of the correction signal, the beam departs from its intended path by a predetermined amount in the direction of the control element associated therewith, and electrons which thereupon impinge upon the control strip are utilized to develop a correction voltage of sui'licient magnitude to substantially overcome the bias. Hence, in the absence of voltage deviations, the beamfollows its intended path.

Themagnitude of the bias referred to above, may be substantially equal to the maximum deection-voltage deviations, of opposite sign to the bias, which are anticipated. Such deviations, when they occur, merely tend to overcome, or at least diminish, the bias and thus cause the beam to withdraw, at leastl partially, from the control strip, thereby diminishing the correction signal developed. The net resultis that the beam remains substantially in its proper vertical position. i

When voltage deviations'of the same sign as the bias occur, the beamtendsto invade the control strip by an increased amo-unt and correction signals of increased magnitude are developed which are effective to overcome substantially the said voltage deviations of same sign.

Suitable switching and feedback means for the biased system abovev described are provided by switch 33, feedback path 3l, amplifier 31, etc., of the circuit illustrated in Figure 1, it being understood that only one switch and one feedback circuit are required for the biased system.

Control means which employ a second electron beam to accomplish results similar to those of the instant invention are described and claimed in a copending application of one of us, namely, Allen C. Munster, led Nov. 23, 1946, Serial No.

"711,969, and assigned to Philco Corporation.

cyclically deilecting said beam successively along a plurality of preselected scanning lines; means responsive to deviations of said beam for generating signals identifiable with the direction oi said deviations, said signals being derived from the change in the electrical potential of a scanning line which is impinged by said beam in deviated position; means for selecting said signals in synchronisrn with said beam deflection; and means for applying said selected signals to said beam in such mannery as `to oppose said deviations.

2. In an electrical system: means for producing a beam of electriiied particles; a first means for cyclically deflecting said beam in one coordinate; a second means for cyclically deflecting said beam in a Vsecond coordinate; a target plate of preselected configuration; means responsive to changes in the electrical potentialof said target plate resulting from bombardment thereof by a beam which has deviated from its intended position in said second coordinate; and means for selectively coupling portions of said responsive means to said secondk deecting means in synchronism with the cyclical movements of said beam.

3. In a cathode-ray system: a screen; means for producing a cathode-ray beam; means for cyclically moving said beam across said screen in successive lines in accordance with a preselected scanning pattern; control elements of conductive material so positioned that during successive portions of said scanning cycle each of said elements is successively positioned substantially parallel with and adjacent to one side of aline then being scanned, and during other successive portions of saidscanning cyclev each of the same said elements is successively positioned substantially parallel with and adjacent to the other side of a different linethen being scanned; means responsive to changesv in the electrical potential of said control elementsfor deriving control signals from the bombardment of said adjacent control elements; and means synchronized with said scanning cycle for utilizing the signal derived from an element adjacent the line then being scanned to move said beam toward said lastnamed line.

4. In a television system; a screen; means for producing an electron beam; means for cyclically scanning said screen with said beam in accordance with a preselected scanning pattern comprised of a plurality of interlaced fields; a plurality of control elements corresponding to said scanning fields; means responsive to changes in the electrical potential of said control elements for deriving signals from the bombardment of said control elements by said beam; means synchronized with said scanning operation: for disregarding signals derived from the bombardment of an element corresponding to the. field then intended to be scanned, and for utilizing signals derived from the bombardment of elements. corresponding to a field not intended to be then scanned, to return said beam; to its intended field.

5. In a televisionsystem; means Yfor generat- Vand in said rst direction from said second field;

means for deriving control voltages from the changes in the electrical potential of said ycontrol elements resulting from bombardment thereof by said beam; and means synchronized with said Adeflection cycle for Vutilizing said control voltages to oppose departure of said beam from the elds of said preselected scanning pattern.

v6. In a television system; a screen; means for producing an electron beam; means for cyclically scanning said screen with said beam in accordance with a preselected 'scanning pattern comprised of a plurality of interlaced elds; control strips of conductive material positioned in the interstices of said scanning lines; means for deriving control signals from the changes in electrical potential of said control strips resulting from the bombardment thereof by said scanning beam; meansv synchronized with the scanning motion of said beam for utilizing signals derived from a control strip when said strip is adjacent one side of a line then being scanned to move Ysaid beam toward said line; and means synchronized with the scanning motion of said beam for utilizing the signals derived from said same control strip Wl'len said strip is adjacent the other side of a different line then being scanned to move said beam toward said different line.

7. In an electrical system: means for generating a beam of electrified particles; means for cyclically deflecting said beam successively along a plurality of preselected scanning lines; means responsive to changes in the electrical potential of said scanning lines caused by deviations of said beam for generating correcting voltages; and means for simultaneously coupling different portions of said responsive means to said deflection means successively in synclironism with said deflection cycle to so modify the operation of said deflection means as to oppose said deviations.

8. In an electrical system: means for generating a beam of electriiied particles; means for cyclically deflecting said beam successively along va plurality of preselected scanning lines; means responsive to deviations of said beam ior deriving control signals from changes in the electrical potential of said scanning lines resulting from impingement thereupon of electrons of said beam when in deviated position; and means synchronized with said beam deflections for coupling different portions of said responsive means diiferently and successively to said Abeam-deilection means so as to oppose said deviations.

ALLEN C. MNSTER..

DAVID E. SUNSTEIN.

REFERENCES CITED The following references are of record in the rile of this patent:

UNITED STATES PATENTS Number Name Date '2,307,188 Bedford Jan. 5, 1943 2,415,059 Zworykin Jan, 28, 1947 

